Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$38.74	11.770%	$43.2997	$43.30	$43.30	$43.30
Purchase #2	$114.53	5.193%	$120.4775	$120.48	$120.50	$120.50
Purchase #3	$182.29	7.853%	$196.6052	$196.61	$196.60	$196.60
Purchase #4	$212.47	10.563%	$234.9132	$234.91	$234.90	$234.90
Purchase #5	$84.38	6.574%	$89.9271	$89.93	$89.95	$89.90
Purchase #6	$148.39	11.810%	$165.9149	$165.91	$165.90	$165.90
Purchase #7	$36.27	5.439%	$38.2427	$38.24	$38.25	$38.20
7 purchase totals =	$817.07		$889.3803	$889.38	$889.40	$889.30